This chapter introduces two techniques for documenting business processes- Data Flow Diagrams (DFD's) and System Flowcharting (SFC). It discusses how to read these documents, their purpose, and guidelines for creating DFD's and SFC's from narratives (see dicussion)----
Data Flow Diagrams:
Types of Dataflow Diagrams (define and explain the differences):
Physical: A graphical representation of a system showing the systems internal and external entities, and the flows of data into and out of these entities. It specifies where, how and by whom a system's processes are accomplished. A physical DFD does not tell us what is being accomplished. The physical DFD's bubbles are labeled with nouns and the data flows are labeled so as to indicate how data are transmitted between bubbles.
Nouns are in bubbles, portrays a system's infrastructure.
Logical: A graphical representation of a system showing the system's processes (as bubbles), data stores, and the flows of data into and out of the processes and data stores. They are used to show what tasks the system is doing without specifying how, where or by whom the tasks are accomplished. The advantage of a logical DFD versus a physical DFD is that we can concentrate on the functions that a system performs.
Verbs are in bubbles, portrays a system's activities.
Levels of Dataflow Diagrams:
Context: A top-level, or least detailed, diagram of an information system that depicts the system and all of its internal activities as a single bubble, and shows the data flows into and out of the system from and to the external entities.
Tracks data from the start to the end of the process
Level-0 - Level-0 DFDs represents a system's major processes, data flows, and data stores at a high level of detail. Level-0 diagram bubbles are numbered with a #.0. For example, 1.0, 2.0, etc.
Level-1 - Level-1 DFDs provide an explosion of a process in a level-0 diagram, breaking it further into a more elementary process. Level-1 diagrams are numbered with a #.#. For example, 1.1, 1.2, etc. Also, the entity boxes that will appear in a context diagram and a level-0 diagram will not usually appear in diagrams below level-0.
Level-x (How low can you go?): A DFD that is the result of x nested decompositions of a series of subprocesses from a process on a level-0 diagran.
Balanced Data Flow Diagram set: When two DFD's-- such as the context and level 0-- have equivalent external data flows (inputs & outputs), we say that the DFDs are balanced. Only balanced sets of DFDs (that is, a context diagram, a logical DFD and a physical DFD) are correct.
Data Flow Diagram Symbols:
Bubble (Physical or Logical): depicts an entity (Physical DFD) or process (Logical DFD) in which incoming data flows are transformed into outgoing flows
Arrow: data flow symbol that represents a pathway for data
Box: external entity symbol that portrays a source or destination of data outside the system
Open-ended Rectangle: data store symbol that represents a place where data are stored
Drawing DFD Guidelines: Drawing the Context Diagram:
1. Include within the system context bubble any entity that processes information
2. Include only normal (routine) processes
3. Include in the diagram all the entities and activities described in the system narrative, and only those described in the narrative~make no assumptions.
4. Chose only one entity to represent activities done by multiple entities. Drawing the Current Physical Data Flow Diagram:
5. Draw a data flow arrow for each flow of data information and label each activity with a number to show the order in which data flows.
6. If a data store is necessary because of delay in processing time, include the data store in the diagram even if the narrative doesn't mention it. Drawing the Current Logical Data Flow Diagram:
7. Group activities that occur at the same place and time.
8. Group activities that occur at the same time, even if they do not occur at the same place.
9. Group activities that are related.
10. Use between 5 and 7 bubbles. Summary of Drawing Data Flow Diagrams:
11. A data flow arrow should point towards a square only if an operation process is to be completed by that entity. A data flow arrow should point towards a bubble only if an information process is to be completed by that entity.
12. On a physical DFD, reading and writing from computer data stores must go through a computer bubble.
13. On a logical DFD, data flows cannot go from higher to lowered numbered bubbles. (i.e. cannot draw a data flow arrow from bubble 3.0 to bubble 2.0)
The Rules when Construction DFDs:
All data flows must begin and end at a process, because simply put the data flows start from a process.
A process cannot have only outputs - "miracle"
A process cannot have only inputs - "black hole"
The inputs of the process must create the outputs from the same process - "gray hole"
all data stores must connect to at least one process
A data store cannot be connected to the initial external entity (source) or the last external entity (sink) of the process
All data flows can have only one direction of flow (separate arrows are used when displaying data flows in and out of the same process)
A forked arrow is used when one data flow leads to two separate processes
Data flows cannot go directly back into the same process it just left.
All data flows must be named using noun phrases.
System Flowcharts:
Definition of System Flowchart: A graphical representation of information processes (activities, logic flows, inputs, outputs, and data storage), as well as the related operation processes (entities, physical flows, and operations activities) It is used to describe the flow of data through a complete data-processing system. Different graphic symbols represent the clerical operations involved and the different input, storage, and output equipment required.
Contrast the information documented in a system flowchart to that in DFD's:
A systems flowchart allows us to see a big picture of a system through the combination of physical and logical aspects of the system. Dataflow diagrams (physical and logical) each represent different phases of a system. The system flowcharts includes the operations process and management context for a system, while these are ignored in the DFDs.
System Flowchart Symbols: (This might be hard since there are many, but if you can copy and paste images here):
Input Symbols - represented by a parallelogram (unless using a specific item such as a document, etc.)
Processing Symbols - represented by a rectangle
Output Symbols - represented by a parallelogram
Data Stores - represented by a cylinder
Connectors - represented by a circle
Miscellaneous -
Drawing System Flowchart Guidelines:
1. Divide and flowchart into labeled columns. Use a seperate column for each internal and external entity.
2. Columns should be positioned so that activities flow from left to right. However, columns should be designed to minimize crossed lines and connectors.
3. Flowchart activities should flow from top to bottom. Put arrows on all flow lines.
4. Attempt to keep the flowchart on one page. If multiple pages must be used, connect the pages with off-page connectors.
5. Within each column, there must be at least one manual process, keying operation, or data store between documents. Documents within the same column can not be directly connected.
6. When crossing organizational lines (i.e., moving from one column to another), show a document as both ends of the flow line unless the connection is so short that the intent is unambigous.
7. Documents or reports printed in a computer facility should be shown in that facility's column first. You can then show the document or report going to the destination unit.
8. Documents or reports printed by a centralized computer facility on equipment located in another organizational unit (e.g., a warehouse or a shipping department) should not be shown within the computer facility.
9. Processing within an organizational unit on devices such as a PC or computerized cash register should be shown within the unit or as a seperate column next to that unit, but not in the central computer facility column.
10. Sequential processing steps (either computerized or manual) with no delay between them (and resulting from the same input) can be shown as one process or as a sequence of processes.
11. The only way to get data into or out of a computer data storage unit is through a computer processing rectangle. For example, if you ket data from a source document, you show a manual keying symbol, a rectangle or square, and then a computer storage unit.
12. A manual process is not needed to show the sending of a document. The sending should be apparent from the movement of the document itself.
13. Do not use a manual process to file a document. Just show the document going into the file.
Summary of Systems Flowcharting:
Strike a balance between clarity and clutter by using annotation judiciously and by using on-page connectors whenever flow lines might create clutter
Avoid crossing lines wherever possible. If you must cross lines, use a "bridge"
Flowchart normal routines and leave exception routines for another page of the flowchart.
Preparing Systems Documentation:
Table of Entities and Activities (describe the steps for creation):
Read through the narrative line by line and while doing so put a circle around all of the activities being performed and put a box around the corresponding entity that is performing that activity. An activity is an action being performed by an internal or external entity. They can include actions related to data or to an operations process. For each activity there must be an entity that performs the activity.
To prepare the table, list the activities that you have previously circled in the order that they are being performed. Along with the activity, list the entity performing that activity and the paragraph number where the activity is described in the narrative.
Once all of the activities are listed, number them consecutively.
Documenting Information Systems:
This chapter introduces two techniques for documenting business processes- Data Flow Diagrams (DFD's) and System Flowcharting (SFC). It discusses how to read these documents, their purpose, and guidelines for creating DFD's and SFC's from narratives (see dicussion)----Data Flow Diagrams:
Types of Dataflow Diagrams (define and explain the differences):
Levels of Dataflow Diagrams:
Data Flow Diagram Symbols:
Drawing DFD Guidelines:
Drawing the Context Diagram:
1. Include within the system context bubble any entity that processes information
2. Include only normal (routine) processes
3. Include in the diagram all the entities and activities described in the system narrative, and only those described in the narrative~make no assumptions.
4. Chose only one entity to represent activities done by multiple entities.
Drawing the Current Physical Data Flow Diagram:
5. Draw a data flow arrow for each flow of data information and label each activity with a number to show the order in which data flows.
6. If a data store is necessary because of delay in processing time, include the data store in the diagram even if the narrative doesn't mention it.
Drawing the Current Logical Data Flow Diagram:
7. Group activities that occur at the same place and time.
8. Group activities that occur at the same time, even if they do not occur at the same place.
9. Group activities that are related.
10. Use between 5 and 7 bubbles.
Summary of Drawing Data Flow Diagrams:
11. A data flow arrow should point towards a square only if an operation process is to be completed by that entity. A data flow arrow should point towards a bubble only if an information process is to be completed by that entity.
12. On a physical DFD, reading and writing from computer data stores must go through a computer bubble.
13. On a logical DFD, data flows cannot go from higher to lowered numbered bubbles. (i.e. cannot draw a data flow arrow from bubble 3.0 to bubble 2.0)
The Rules when Construction DFDs:
All data flows must begin and end at a process, because simply put the data flows start from a process.
System Flowcharts:
Definition of System Flowchart: A graphical representation of information processes (activities, logic flows, inputs, outputs, and data storage), as well as the related operation processes (entities, physical flows, and operations activities) It is used to describe the flow of data through a complete data-processing system. Different graphic symbols represent the clerical operations involved and the different input, storage, and output equipment required.
Contrast the information documented in a system flowchart to that in DFD's:
A systems flowchart allows us to see a big picture of a system through the combination of physical and logical aspects of the system. Dataflow diagrams (physical and logical) each represent different phases of a system. The system flowcharts includes the operations process and management context for a system, while these are ignored in the DFDs.
System Flowchart Symbols: (This might be hard since there are many, but if you can copy and paste images here):
Flow Chart ImagesDrawing System Flowchart Guidelines:
1. Divide and flowchart into labeled columns. Use a seperate column for each internal and external entity.2. Columns should be positioned so that activities flow from left to right. However, columns should be designed to minimize crossed lines and connectors.
3. Flowchart activities should flow from top to bottom. Put arrows on all flow lines.
4. Attempt to keep the flowchart on one page. If multiple pages must be used, connect the pages with off-page connectors.
5. Within each column, there must be at least one manual process, keying operation, or data store between documents. Documents within the same column can not be directly connected.
6. When crossing organizational lines (i.e., moving from one column to another), show a document as both ends of the flow line unless the connection is so short that the intent is unambigous.
7. Documents or reports printed in a computer facility should be shown in that facility's column first. You can then show the document or report going to the destination unit.
8. Documents or reports printed by a centralized computer facility on equipment located in another organizational unit (e.g., a warehouse or a shipping department) should not be shown within the computer facility.
9. Processing within an organizational unit on devices such as a PC or computerized cash register should be shown within the unit or as a seperate column next to that unit, but not in the central computer facility column.
10. Sequential processing steps (either computerized or manual) with no delay between them (and resulting from the same input) can be shown as one process or as a sequence of processes.
11. The only way to get data into or out of a computer data storage unit is through a computer processing rectangle. For example, if you ket data from a source document, you show a manual keying symbol, a rectangle or square, and then a computer storage unit.
12. A manual process is not needed to show the sending of a document. The sending should be apparent from the movement of the document itself.
13. Do not use a manual process to file a document. Just show the document going into the file.
Summary of Systems Flowcharting:
Preparing Systems Documentation:
Table of Entities and Activities (describe the steps for creation):